Biology subjects

Hernandez, C. J.

Publications and source records attributed to Hernandez, C. J..

3 recordsLinked to original sources

bioRxiv2023

Solute Transport in Engineered Living Materials using Bone Inspired Microscale Channel Networks

Engineered living materials (ELMs) are an emerging class of materials that is synthesized and/or populated by living cells. Maintaining living cells within an ELM over prolonged periods remains a major technical challenge that limits the service life of a material. Biological materials regularly maintain robust populations of living cells. Bone maintains living cells for decades by delivering nutrients through a network of nanoscale channels punctuated by microscale pores. Nutrient transfer in bone is enabled by mechanical loading experienced during regular use. Here we identify the characteristics of channel-pore network geometries and external mechanical loading that can be used in engineered living materials to deliver nutrients to resident cell populations. Transport occurs when deformation in the microscale pore network exceeds the volume of the connecting channels. Computational models show that transport is enhanced at greater load magnitudes and lower loading frequencies and are consistent with experimental validation using microfluidic systems. Our findings provide quantitative design principles for channel-pore networks capable of delivering nutrients to materials designed to house living cells.

bioengineering↗

bioRxiv2023

Deficiency of macrophage-derived Dnase1L3 causes lupus-like phenotypes in mice

Systemic Lupus Erythematosus (SLE) is a chronic autoimmune disease caused by environmental factors and loss of key proteins. One such protein is a serum endonuclease secreted by macrophages and dendritic cells, Dnase1L3. Loss of Dnase1L3 causes pediatric-onset lupus in humans is Dnase1L3. Reduction in Dnase1L3 activity occurs in adult-onset human SLE. However, the amount of Dnase1L3 necessary to prevent lupus onset, if the impact is continuous or requires a threshold, and which phenotypes are most impacted by Dnase1L3 remain unknown. To reduce Dnase1L3 protein levels, we developed a genetic mouse model with reduced Dnase1L3 activity by deleting Dnase1L3 from macrophages (cKO). Serum Dnase1L3 levels were reduced 67%, though Dnase1 activity remained constant. Sera were collected weekly from cKO and littermate controls until 50 weeks of age. Homogeneous and peripheral anti-nuclear antibodies were detected by immunofluorescence, consistent with anti-dsDNA antibodies. Total IgM, total IgG, and anti-dsDNA antibody levels increased in cKO mice with increasing age. In contrast to global Dnase1L3-/- mice, anti-dsDNA antibodies were not elevated until 30 weeks of age. The cKO mice had minimal kidney pathology, except for deposition of immune complexes and C3. Based on these findings, we conclude that an intermediate reduction in serum Dnase1L3 causes mild lupus phenotypes. This suggest that macrophage-derived DnaselL3 is critical to limiting lupus.

immunology↗

bioRxiv2022

Mechanical stimuli activate gene expression via a cell envelope stress sensing pathway

In tissues with mechanical function, the regulation of remodeling and repair processes is often controlled by mechanosensitive mechanisms; damage to the tissue structure is detected by changes in mechanical stress and strain, stimulating matrix synthesis and repair. While this mechanoregulatory feedback process is well recognized in animals and plants, it is not known whether such a process occurs in bacteria. In Vibrio cholerae, antibiotic-induced damage to the load-bearing cell wall promotes increased signaling by the two-component system VxrAB, which stimulates cell wall synthesis. Here we show that changes in mechanical stress and strain within the cell envelope are sufficient to stimulate VxrAB signaling in the absence of antibiotics. We applied mechanical forces to individual bacteria using three distinct loading modalities: extrusion loading within a microfluidic device, compression, and hydrostatic pressure. In all three cases, VxrAB signaling, as indicated by a fluorescent protein reporter, was increased in cells submitted to greater magnitudes of mechanical loading, hence diverse forms of mechanical stimuli activate VxrAB signaling. Mechanosensitivity of VxrAB signaling was lost following removal of the VxrAB stimulating endopeptidase ShyA, suggesting that VxrAB may not be directly sensing mechanical forces, but instead relies on other factors including lytic enzymes in the periplasmic space. Our findings suggest that mechanical signals play an important role in regulating cell wall homeostasis in bacteria. Significance StatementBiological materials with mechanical function (bones, muscle, etc.) are often maintained through mechanosensitive mechanisms, in which damage-induced reductions in stiffness stimulate remodeling and repair processes that restore mechanical function. Here we show that a similar process can occur in bacteria. We find that mechanical stresses in the bacterial cell envelope (the primary load-bearing structure in bacteria) regulate signaling of a two-component system involved in cell wall synthesis. These findings suggest that the mechanical stress state within the cell envelope can contribute to cell wall homeostasis. Furthermore, these findings demonstrate the potential to use mechanical stimuli to regulate gene expression in bacteria.

microbiology↗